1. Field of the Invention
This invention relates to a method and apparatus for reading out a radiation image from a stimulable phosphor sheet, on which the radiation image has been stored, to obtain an image signal representing the radiation image.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then exposed to stimulating rays, such as a laser beam, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is guided by a light guide member and photoelectrically detected with photoelectric read-out means, such as a photomultiplier (hereinbelow referred to as the PMT), and converted into an electric image signal. The image signal is then processed and used for the reproduction of the radiation image of the object as a visible image on a recording material.
The applicant proposed built-in types of radiation image recording and read-out apparatuses, comprising: (i) circulation and conveyance means for conveying at least one stimulable phosphor sheet along a circulation path, (ii) an image recording section, which is located in the circulation path and in which a radiation image of an object is stored on the stimulable phosphor sheet, (iii) an image read-out section, which is located in the circulation path and in which the radiation image is read out from the stimulable phosphor sheet, and (iv) an erasing section, which is located in the circulation path and in which energy remaining on the stimulable phosphor sheet after the radiation image has been read out therefrom is released. The built-in types of radiation image recording and read-out apparatuses are disclosed in, for example, U.S. Patent Nos. 4,543,479 and 4,851,679, and Japanese Unexamined Patent Publication No. 3(1991)-238441. With the proposed built-in types of radiation image recording and read-out apparatuses, the stimulable phosphor sheet is utilized repeatedly and is processed efficiently.
Also, a different example of the built-in type of radiation image recording and read-out apparatus is proposed in, for example, Japanese Patent Publication No. 6(1994)-5358. In the proposed built-in type of radiation image recording and read-out apparatus, a stimulable phosphor sheet is kept stationary, and a read-out and erasing unit, which comprises an image read-out section and an erasing section combined into an integral body, is reciprocally moved with respect to the stimulable phosphor sheet. Also, a radiation image read-out operation is performed in the course of forward movement of the readout and erasing unit, and an erasing operation for releasing energy remaining on the stimulable phosphor sheet is performed in the course of backward movement of the read-out and erasing unit. In the proposed radiation image recording and read-out apparatus, the stimulating rays are irradiated to the surface of the stimulable phosphor sheet, which surface is opposite to the radiation irradiation side surface of the stimulable phosphor sheet, the light, which is emitted from the opposite surface of the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the stimulating rays, is detected photoelectrically, and the radiation image is thereby read out from the stimulable phosphor sheet.
However, with the radiation image recording and read-out apparatus proposed in Japanese Patent Publication No. 6(1994)-5358, wherein the stimulating rays are irradiated to the surface of the stimulable phosphor sheet, which surface is opposite to the radiation irradiation side surface of the stimulable phosphor sheet, the intensity of the light, which is emitted by the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the stimulating rays, is low. Therefore, the problems occur in that an image signal having a high signal-to-noise ratio cannot be obtained.
The primary object of the present invention is to provide a radiation image recording and read-out method, wherein stimulating rays are irradiated to a surface of a stimulable phosphor sheet, which surface is opposite to a radiation irradiation side surface of the stimulable phosphor sheet, and wherein an image signal having a high signal-to-noise ratio is capable of being obtained.
Another object of the present invention is to provide an apparatus for carrying out the radiation image recording and read-out method.
The present invention provides a radiation image recording and read-out method, comprising the steps of:
i) exposing a stimulable phosphor sheet, which is capable of storing a radiation image thereon, to radiation, which carries image information of an object, in order to store a radiation image of the object on the stimulable phosphor sheet,
ii) exposing the stimulable phosphor sheet, on which the radiation image has been stored, to stimulating rays, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation, the stimulating rays being irradiated to a surface of the stimulable phosphor sheet, which surface is opposite to a radiation irradiation side surface of the stimulable phosphor sheet, and photoelectrically detecting the light, which is emitted from the two surfaces of the stimulable phosphor sheet, with photoelectric read-out means in order to read out the radiation image and to obtain image signals representing the radiation image,
iii) releasing residual energy, which remains on the stimulable phosphor sheet after the radiation image has been read out therefrom, and
iv) reciprocally moving an image read-out section, in which the step of reading out the radiation image is performed, and an erasing section, in which the step of releasing the residual energy remaining on the stimulable phosphor sheet is performed, together with each other with respect to the stimulable phosphor sheet.
In the radiation image recording and read-out method in accordance with the present invention, in the step of reciprocally moving the image read-out section and the erasing section together with each other with respect to the stimulable phosphor sheet, the image read-out section and the erasing section may be moved together with each other while the stimulable phosphor sheet is being kept stationary. Alternatively, the stimulable phosphor sheet may be moved while the image read-out section and the erasing section are being kept stationary. As another alternative, both the stimulable phosphor sheet and the image read-out section, the erasing section may be moved.
The radiation image recording and read-out method in accordance with the present invention should preferably be modified such that the radiation image readout from the two surfaces of the stimulable phosphor sheet is performed in the course of forward movement in the reciprocal movement, and the releasing of the residual energy is performed in the course of backward movement in the reciprocal movement.
Alternatively, the radiation image recording and read-out method in accordance with the present invention should may be modified such that the radiation image readout from the two surfaces of the stimulable phosphor sheet is performed in the course of forward movement in the reciprocal movement, and the releasing of the residual energy is performed in the course of the forward movement in the reciprocal movement. In such cases, the releasing of the residual energy should preferably be further performed in the course of backward movement in the reciprocal movement.
Also, the radiation image recording and read-out method in accordance with the present invention should preferably be modified such that, when the storing of the radiation image on the stimulable phosphor sheet is to be performed, photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, is retreated from the radiation irradiation side surface of the stimulable phosphor sheet.
For such purposes, the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, may be moved while the stimulable phosphor sheet is being kept stationary. Alternatively, the stimulable phosphor sheet may be moved while the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, is being kept stationary. As another alternative, both the stimulable phosphor sheet and the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, may be moved.
Further, in the radiation image recording and read-out method in accordance with the present invention, photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, should preferably be a long photomultiplier, means provided with a light guide member having flexibility (constituted of an optical fiber, or the like), or a semiconductor sensor.
Furthermore, in the radiation image recording and read-out method in accordance with the present invention, the stimulable phosphor sheet should preferably have anisotropy in a thickness direction of the stimulable phosphor sheet.
Also, in the radiation image recording and read-out method in accordance with the present invention, the stimulable phosphor sheet should preferably contain a coloring agent, which transmits only the light emitted by the stimulable phosphor sheet and absorbs the stimulating rays.
The present invention also provides an apparatus for carrying out the radiation image recording and read-out method in accordance with the present invention. Specifically, the present invention also provides a radiation image recording and read-out apparatus, comprising:
i) an image recording section for exposing a stimulable phosphor sheet, which is capable of storing a radiation image thereon, to radiation, which carries image information of an object, in order to store a radiation image of the object on the stimulable phosphor sheet,
ii) an image read-out section provided with:
a stimulating ray source for producing stimulating rays and irradiating the stimulating rays to the stimulable phosphor sheet, on which the radiation image has been stored, the stimulating rays being irradiated to a surface of the stimulable phosphor sheet, which surface is opposite to a radiation irradiation side surface of the stimulable phosphor sheet, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation, and
photoelectric read-out means for photoelectrically detecting the light, which is emitted from the two surfaces of the stimulable phosphor sheet, in order to read out the radiation image and to obtain image signals representing the radiation image,
iii) an erasing section for releasing residual energy, which remains on the stimulable phosphor sheet after the radiation image has been read out therefrom in the image read-out section, and
iv) movement means for reciprocally moving the image read-out section and the erasing section together with each other with respect to the stimulable phosphor sheet.
In the radiation image recording and read-out apparatus in accordance with the present invention, with the movement means, the image read-out section and the erasing section may be moved together with each other while the stimulable phosphor sheet is being kept stationary. Alternatively, with the movement means, the stimulable phosphor sheet may be moved while the image read-out section and the erasing section are being kept stationary. As another alternative, with the movement means, both the stimulable phosphor sheet and the image read-out section, the erasing section may be moved.
The radiation image recording and read-out apparatus in accordance with the present invention should preferably be modified such that the radiation image read-out from the two surfaces of the stimulable phosphor sheet is performed in the course of forward movement in the reciprocal movement, and the releasing of the residual energy by the erasing section is performed in the course of backward movement in the reciprocal movement.
Alternatively, the radiation image recording and read-out apparatus in accordance with the present invention should may be modified such that the radiation image readout from the two surfaces of the stimulable phosphor sheet is performed in the course of forward movement in the reciprocal movement, and the releasing of the residual energy by the erasing section is performed in the course of the forward movement in the reciprocal movement. In such cases, the releasing of the residual energy by the erasing section should preferably be further performed in the course of backward movement in the reciprocal movement.
Also, the radiation image recording and read-out apparatus in accordance with the present invention should preferably further comprise retreating means for operating such that, when the storing of the radiation image on the stimulable phosphor sheet is to be performed, the retreating means retreats photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, from the radiation irradiation side surface of the stimulable phosphor sheet.
With the retreating means, the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, may be moved while the stimulable phosphor sheet is being kept stationary. Alternatively, with the retreating means, the stimulable phosphor sheet may be moved while the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, is being kept stationary. As another alternative, with the retreating means, both the stimulable phosphor sheet and the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, may be moved.
Further, in the radiation image recording and read-out apparatus in accordance with the present invention, photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, should preferably be a long photomultiplier, means provided with a light guide member having flexibility (constituted of an optical fiber, or the like), or a semiconductor sensor.
Furthermore, in the radiation image recording and read-out apparatus in accordance with the present invention, the stimulable phosphor sheet should preferably have anisotropy in a thickness direction of the stimulable phosphor sheet.
Also, in the radiation image recording and read-out apparatus in accordance with the present invention, the stimulable phosphor sheet should preferably contain a coloring agent, which transmits only the light emitted by the stimulable phosphor sheet and absorbs the stimulating rays.
With the radiation image recording and read-out method and the radiation image recording and read-out apparatus in accordance with the present invention, the stimulating rays are irradiated to the surface of the stimulable phosphor sheet, which surface is opposite to the radiation irradiation side surface of the stimulable phosphor sheet, and the light, which is emitted from each of the two surfaces of the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the stimulating rays, is photoelectrically detected. In this manner, the readout of the radiation image is performed. Therefore, the efficiency, with which the light emitted by the stimulable phosphor sheet is collected, is capable of being enhanced. The two image signals having been detected from the two surfaces of the stimulable phosphor sheet may then be added to each other, and an image signal having an enhanced signal-to-noise ratio can thereby be obtained.
With the radiation image recording and read-out method and the radiation image recording and read-out apparatus in accordance with the present invention, wherein the radiation image readout from the two surfaces of the stimulable phosphor sheet is performed in the course of the forward movement in the reciprocal movement of the image read-out section and the erasing section, and the releasing (i.e., the erasing) of the residual energy is performed in the course of backward movement in the reciprocal movement, the radiation image readout and the releasing of the residual energy are capable of being performed efficiently.
With the radiation image recording and read-out method and the radiation image recording and read-out apparatus in accordance with the present invention, wherein the radiation image readout and the releasing of the residual energy are performed simultaneously in the course of the forward movement in the reciprocal movement, the radiation image readout and the releasing of the residual energy can be performed with one time of movement. Therefore, the radiation image readout and the releasing of the residual energy can be performed more efficiently. In such cases, the releasing of the residual energy may further be performed in the course of the backward movement in the reciprocal movement. In this manner, even if the dose of radiation delivered to the stimulable phosphor sheet is large and therefore the residual energy cannot be released sufficiently in the course of the forward movement alone in the reciprocal movement, the residual energy remaining on the stimulable phosphor sheet is capable of being released reliably.
With the radiation image recording and read-out method and the radiation image recording and read-out apparatus in accordance with the present invention, when the storing of the radiation image on the stimulable phosphor sheet is to be performed, the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, may be retreated from the radiation irradiation side surface of the stimulable phosphor sheet. In such cases, the problems do not occur in that the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, is exposed to the radiation. Therefore, the photoelectric read-out means is capable of being prevented from becoming impoverished by the radiation.
With the radiation image recording and read-out method and the radiation image recording and read-out apparatus in accordance with the present invention, wherein the photoelectric read-out means, which is located at the radiation irradiation side surface of the stimulable phosphor sheet, is a long photomultiplier, means provided with a light guide member having flexibility, or a semiconductor sensor, the space required to locate the photoelectric read-out means at the radiation irradiation side surface of the stimulable phosphor sheet is capable of being kept small. Therefore, the size of the radiation image recording and read-out apparatus can be kept small.
With the radiation image recording and read-out method and the radiation image recording and read-out apparatus in accordance with the present invention, wherein the stimulable phosphor sheet has anisotropy in the thickness direction of the stimulable phosphor sheet, scattering of the stimulating rays within the stimulable phosphor sheet can be prevented, and an image signal representing an image of a high resolution can thereby obtained.
With the radiation image recording and read-out method and the radiation image recording and read-out apparatus in accordance with the present invention, wherein the stimulable phosphor sheet contains the coloring agent, which transmits only the light emitted by the stimulable phosphor sheet and absorbs the stimulating rays, scattering of the stimulating rays within the stimulable phosphor sheet can be prevented, and an image signal representing an image of a high resolution can thereby obtained.